The present invention relates to a constant velocity universal joint that is suited to applications where rotation backlash is undesirable, and is particularly preferable for the steering apparatus of an automobile.
In the steering apparatus of an automobile, for example as shown schematically in FIG. 34, rotation torque imparted to a steering wheel 20 is transmitted via a main shaft 21 of a steering column and an intermediate shaft 22 to a gear shaft (pinion shaft or the like) 24 of a steering gear 23, while being converted to a linear motion by the mechanism of the steering gear 23 thereby to be transmitted via a link mechanism (knuckle or the like) 25 to wheels 26 as steering force. The steering gear 23 may be one of various types including rack and pinion type, ball screw type and worm roller type, while the rack and pinion type is predominantly used for the reason of high rigidity and light weight thereof. The intermediate shaft 22 is disposed at an angle to the main shaft 21 and the gear shaft 24, and is connected to the main shaft 21 and the gear shaft 24 via universal joints 27, 28, for the purpose of absorbing the impact energy in case of collision.
While the Cardan joint (universal joint employing cross yokes) has been predominantly used for the universal joints (27, 28) of the steering apparatus, constant velocity universal joints are being increasingly employed instead of the Cardan joint in order to allow a larger angle in the joint (in conjunction with the layout of vehicle components) and improve the movement of the joint (feel of the steering operation).
Meanwhile a constant velocity universal joint of ordinary constitution has a small clearance (inner gap) between torque transmitting ball and a ball track, which inevitably results in rotation backlash (play in the circumferential direction) taking place in the joint when the direction of rotation changes. Thus use of the constant velocity universal joint of the ordinary constitution in the steering apparatus leads to such problems as the loss of stability in steering, and loss of sharp or direct feel of steering.
In the field of automobile, constant velocity universal joints have many records of applications to the drive shaft, and the constant velocity universal joint of the ordinary constitution is normally designed to such specifications that satisfy the requirements of the drive shaft. In the case of the steering apparatus, however, since less load torque is applied to the joint and the joint rotates at lower speeds than the drive shaft, the constant velocity universal joint of the ordinary constitution has rather excessively higher specifications compared to the required characteristics, and therefore improvements are required for the reduction of joint weight and manufacturing cost.
The ball fixed type constant velocity universal joint of this type also requires the complicated assembly process as described above, and therefore has such disadvantages as follows.
(1) The assembly work requires skilled technique and is difficult to mechanize (automate).
(2) It is necessary to make the guide grooves of the inner and outer joint members longer (in the axial direction) than the length required for the function, in order to facilitate the assembly of the balls, thus resulting in larger joint dimension.
(3) It is necessary to make the size of the pocket of the cage in the circumferential direction larger, in order to facilitate the assembly of the balls (because the balls move in the circumferential direction in the pocket of the cage when the inner and outer joint members are caused to make angular displacement). This makes a disadvantage in the design of the cage in terms of strength.
(4) It is necessary to prepare the inner joint member and the shaft separately (in case the inner joint member and the shaft are prepared as an integral part, the shaft interferes with the outer joint member when assembling the balls, thus making it impossible to secure the amount of angular displacement required for the assembly). This leads to increases in the number of parts and in the number of assembly steps.
An object of the present invention is to solve the problem of rotation backlash in the ball fixed type constant velocity universal joint, and provide a simpler, light weight, compact and low-cost ball fixed type constant velocity universal joint that can be assembled in an improved process.
Another object of the present invention is to ensure good feel of rotation (smoothness of rotation) and, when applied to the steering apparatus in particular, improve the performance such as the feel of steering, while maintaining the constant velocity characteristics of this type of constant velocity universal joint.
Yet another object of the present invention is to reduce the resistance to the rotation in the constant velocity universal joint of this type and ensure good feel of rotation (smoothness of rotation) and, when used in a steering apparatus in particular, improve the performance such as the steering force, auto-centering of the steering wheel and the feel of steering.
In order to achieve the objects described above, the present invention provides a ball fixed type constant velocity universal joint comprising an outer joint member having a curved guide groove formed in the axial direction on a spherical inner circumferential surface thereof, an inner joint member having a curved guide groove formed in the axial direction on a spherical outer circumferential surface thereof, ball disposed in a ball track formed by the coordination of the guide groove of the outer joint member and the guide groove of the inner joint member, and a cage that holds the ball, with the center of the guide groove of the outer joint member and the center of the guide groove of the inner joint member being offset to the opposite sides to each other by equal distances in the axial direction with respect to the center plane of the joint that include the centers of the ball, the ball track being gradually reduced toward the opening or the innermost side of the joint, wherein the inner joint member is allowed to make relative displacement in the axial direction with respect to the cage, and elastic pressing means having a spherical surface that makes fitting contact with the outer circumferential surface of the inner joint member is interposed between the outer circumferential surface of the inner joint member and the inner circumferential surface of the cage, so that the elastic force of the elastic pressing means presses the outer circumferential surface of the inner joint member toward the side opposite to the offset direction of center of the guide groove thereof.
The inner joint member makes a relative displacement in the axial direction opposite to the offset direction under the urging pressure of the elastic pressing means, thereby to press the ball, and stops at a position where the inner gap between the balls and the guide grooves of the inner and outer joint members disappears. As a result, a certain amount of preload is applied in the axial direction to the ball, thus eliminating the rotation backlash (play in the circumferential direction). Also because the spherical surface of the elastic pressing means presses the outer circumferential surface of the inner joint member, the surface pressure in the portion of contact between both members is reduced and the outer circumferential surface of the inner joint member can be guided by the spherical surface.
In the constitution described above, the ball track may have such a configuration that is gradually reduced toward the opening side of the joint, at least the region on the opening side of the inner circumferential surface of the cage is a cylindrical surface that fits with the outer circumferential surface of the inner joint member, and the elastic pressing means is disposed on the cylindrical surface. This configuration makes it possible to assemble the inner joint member into the inner circumferential surface of the cage after assembling the cage and the ball into the outer joint member.
In addition to the constitution described above, the region on the opening side of the inner circumferential surface of the outer joint member may have a cylindrical surface that fits with the outer circumferential surface of the cage. This configuration makes it easier to assemble the cage into the outer joint member.
Since the inner joint member can be assembled after assembling the cage and the balls in the outer joint member, it is made possible to integrate the inner joint member and the shaft (to form in an integral part, or bond together) thereby decreasing the number of parts and the number of assembly steps, without causing any trouble in the assembly operation.
Further, in order to achieve the objects described above, the present invention provides a ball fixed type constant velocity universal joint comprising an outer joint member having a curved guide groove formed in the axial direction on a spherical inner circumferential surface thereof, an inner joint member having a curved guide groove formed in the axial direction on a spherical outer circumferential surface thereof, ball disposed in ball track formed by the coordination of the guide groove of the outer joint member and the guide groove of the inner joint member, and a cage that holds the ball, with the center of the guide groove of the outer joint member and the center of the guide groove of the inner joint member being offset to the opposite sides to each other by equal distances in the axial direction with respect to the center plane of the joint that includes the center of the ball, the ball track being gradually reduced toward the opening or the innermost side of the joint, wherein at least the region on the opening side of the inner circumferential surface of the cage is formed in a cylindrical surface that fits the outer circumferential surface of the inner joint member, and a retaining member having a spherical portion that makes fitting contact with the outer circumferential surface of the inner joint member is disposed on the cylindrical surface. This type constant velocity universal joint can be used for a connection joint for drive shafts, propeller shafts or the like of automobile, in addition to steering apparatus.
This configuration makes it possible to assemble the inner joint member into the inner circumferential surface of the cage after assembling the cage and the ball into the outer joint member, by forming at least the region on the opening side of the inner circumferential surface of the cage in a cylindrical surface that fits the outer circumferential surface of the inner joint member. After being assembled in the inner circumferential surface of the cage, the inner joint member is retained in place by the retaining member that is disposed on the cylindrical surface of the cage. The outer circumferential surface of the inner joint member is guided by the spherical portion of the retaining member.
In addition to the constitution described above, the region on the opening side of the inner circumferential surface of the outer joint member may also be formed in a cylindrical surface that fits the outer circumferential surface of the cage. This configuration makes it easier to assemble the cage into the outer joint member.
Since the inner joint member can be assembled after assembling the cage and the ball in the outer joint member, it is made possible to integrate the inner joint member and the shaft (to form in an integral part, or bond together) thereby decreasing the number of parts and the number of assembly steps, without causing any trouble in the assembling operation.
Also, in order to achieve the objects described above, the present invention provides a constant velocity universal joint comprising an outer joint member having a curved guide groove formed in the axial direction on a spherical inner circumferential surface thereof, the guide groove having center of curvature at a point (O1) that is offset by a predetermined distance (f1) from the center of curvature of the spherical inner circumferential surface to one side in the axial direction, an inner joint member having a curved guide groove formed in the axial direction on a spherical outer circumferential surface thereof, the guide groove having center of curvature at a point (O2) that is offset by a predetermined distance (f2) from the center of curvature of the spherical outer circumferential surface to the other side in the axial direction, a ball track formed by the coordination of the guide groove of the outer joint member and the guide groove of the inner joint member that opposes the former, the ball track having wedge-like shape that reduces toward the other side in the axial direction, torque transmitting ball disposed in the ball track, a cage that holds the torque transmitting ball, and preloading means that reduces a clearance between the torque transmitting balls and the ball track by causing an elastic relative displacement to take place in the axial direction between at least one of the outer joint member and the inner joint member and the torque transmitting ball, wherein the offset distance (f1) of the center of curvature (O1) of the guide groove of the outer joint member and the offset distance (f2) of the center of curvature (O2) of the guide groove of the inner joint member are set to have different values, and such a configuration is employed as the center of curvature (O1) and the center of curvature (O2) are offset to the opposite sides by the same distances (f) in the axial direction with respect to the center plane of the joint that includes the center of the torque transmitting ball, when the clearance is reduced by the preloading means.
Specific embodiments of the preloading means may be, for example, (1) to have the torque transmitting ball undergo a displacement in the axial direction toward the reduced side of the ball track, (2) to have the inner joint member undergo a displacement in the axial direction opposite to the offset direction of the center of curvature of the guide groove thereof, (3) to have the outer joint member undergo a displacement in the axial direction to the offset direction of the center of curvature of the guide groove thereof, or (4) to have the inner joint member undergo a displacement in the axial direction opposite to the offset direction of the center of curvature of the guide groove thereof and to have the outer joint member undergo a displacement in the axial direction to the offset direction of the center of curvature of the guide groove thereof.
Relation of inequality and difference between the offset distance (f1) of the center of curvature (O1) of the guide groove of the outer joint member and the offset distance (f2) of the center of curvature (O2) of the guide groove of the inner joint member are set by taking into consideration the mode of preloading, the amount of inner gap (the amount of rotation backlash: play in the circumferential direction), presence and size of clearance between the torque transmitting ball and the cage and other factors, so that the center of curvature (O1) and the center of curvature (O2) are offset to the opposite sides by the same distances (f) in the axial direction with respect to the center plane of the joint that includes the center of the torque transmitting ball when the clearance is reduced by the preloading means. This makes it possible to achieve good feel of rotation (smoothness of rotation) while maintaining the constant velocity characteristics of the joint. Relation between the offset distance (f1) and the offset distance (f2) may be set to satisfy f1 greater than f2, or to satisfy f1 less than f2.
The preloading means may be constituted from, for example, a clearance provided in the axial direction between the inner joint member and the cage, and an elastic member that is interposed between the inner joint member and the cage and presses the inner joint member in a direction opposite to the offset direction of the center of the guide groove of the inner joint member. In this case, under the pressing force of the elastic member applied thereto, the inner joint member makes a relative displacement in the axial direction opposite to the offset direction of the center of curvature of the guide groove thereby to press the torque transmitting ball, and stops at a position where the inner gap between the torque transmitting balls and the guide groove (ball track) of the inner and outer joint members disappears. As a result, a certain amount of preload is applied in the axial direction to the torque transmitting ball, thus eliminating the rotation backlash (play in the circumferential direction).
Regions that are free of undercut may be provided in the guide grooves of the outer joint member and the inner joint member. This makes it possible to increase the operating angle of the joint.
The region on the opening side of the inner circumferential surface of the outer joint member may be formed in a cylindrical surface that fits with the outer circumferential surface of the cage. This makes it easier to assemble the cage into the outer joint member.
The constant velocity universal joint of the present invention is light in weight, small in size and low cost, and rotates smoothly without backlash while being capable of taking a large operating angle, and is therefore particularly preferable for the steering apparatus of an automobile.
Also, in order to solve the problems described above, the present invention provides a constant velocity universal joint comprising an outer joint member having a curved guide groove formed in the axial direction on a spherical inner circumferential surface thereof, an inner joint member having a curved guide groove formed in the axial direction on a spherical outer circumferential surface thereof, a ball track formed by the coordination of the guide groove of the outer joint member and the guide groove of the inner joint member that opposes the former, the ball track having wedge-like shape that reduces toward one side in the axial direction, torque transmitting ball disposed in the ball track, a cage having a pocket that holds the torque transmitting ball, and preloading means that reduces the clearance between the torque transmitting balls and the ball track, wherein the clearance xcex4 of the pocket in the axial direction between the pocket of the cage and the torque transmitting ball is set in a range of 0xe2x89xa6xcex4xe2x89xa655 xcexcm.
The reason for setting the clearance xcex4 of the pocket in the axial direction in the range of 0xe2x89xa6xcex4xe2x89xa655 xcexcm is as follows. In the constant velocity universal joint of this type (ball fixed type constant velocity universal joint), the clearance xcex4 of the pocket in the axial direction is normally set to be xcex4 less than 0 (negative clearance) thereby allowing a slight tightening allowance between the pocket of the cage and the torque transmitting ball, in view of the importance placed on the function of the cage to guide the torque transmitting ball (function to keep the torque transmitting ball in the bisecting plane (xcex8/2) of the operating angle xcex8, thereby to ensure constant velocity characteristic of the joint). However, since setting the clearance xcex4 of the pocket in the axial direction to a negative value makes it difficult for the torque transmitting ball to roll over the ball track, this setting has a disadvantage in terms of the resistance to rotation (torque) when the joint of this type transmits rotation torque while taking an operation angle. Resistance of the joint to rotation affects the performance such as the steering force and auto-centering capability in a steering apparatus, and is preferably as small as possible. Although rolling performance of the torque transmitting balls can be improved thereby decreasing the resistance of the joint to rotation by setting the clearance xcex4 of the pocket in the axial direction to be xcex4xe2x89xa70 (positive clearance), making the clearance xcex4 of the pocket in the axial direction too large leads to a decrease in the capability of the cage to guide the torque transmitting ball, resulting in the loss of the constant velocity characteristic of the joint. In the steering apparatus, loss of the constant velocity characteristic of the joint leads to the generation of unusual sound and deterioration in the feel of steering such as hitch. Therefore, it is necessary to set the clearance xcex4 of the pocket in the axial direction in an optimum range in order to reduce the resistance of the joint to rotation and achieve good feel of steering (smoothness of rotation).
Accordingly, a test was conducted to determine the optimum range of the clearance xcex4 of the pocket in the axial direction. The results are shown in Table 1. The test was conducted on the constant velocity universal joint of this embodiment shown in FIG. 1 and FIG. 2. Sample joints having different sizes of clearance xcex4 of the pocket (xcex4=Lxe2x88x92DBALL: refer to FIG. 6) in the axial direction were fabricated and tested to evaluate the resistance to rotation and the feel of steering (smoothness of rotation) under a predetermined operating angle xcex8 and a predetermined magnitude of rotation torque applied thereto. The resistance to rotation was evaluated by whether it was greater or smaller than a criterion. The feel of steering was rated as ◯ when a criterion was exceeded, xcex94 when the criterion was missed with a little margin and ▴ when the criterion could not be reached with a large margin. Comprehensive evaluation which combined the resistance to rotation and the feel of steering was rated as ◯ when the total criterion was reached or xcex94 when not.
As will be apparent from the test results, satisfactory performance was achieved in both the resistance to rotation and the feel of steering when the clearance xcex4 of the pocket in the axial direction was set in a range of 0xe2x89xa6xcex4xe2x89xa655 xcexcm. When xcex4 less than 0, resistance of the joint to rotation increases because it becomes difficult for the torque transmitting balls to roll. When xcex4 greater than 55 xcexcm, on the other hand, the joint cannot operate with satisfactory constant velocity characteristic, thus resulting in poorer feel of steering with such impression as hitch. In view of reducing the resistance of the joint to rotation and achieving good feel of steering (smoothness of rotation) while maintaining the constant velocity characteristic, the optimum range for the clearance xcex4 of the pocket in the axial direction is 0xe2x89xa6xcex4xe2x89xa655 xcexcm.
The preloading means reduces the inner clearance provided between the torque transmitting ball and the ball track by causing a relative displacement between any two components among the outer joint member, the inner joint member, the cage and the torque transmitting ball. The preloading means may be constituted from, for example, a clearance provided in the axial direction between the inner joint member and the cage, and an elastic member that is interposed between the inner joint member and the cage and presses the inner joint member in a direction opposite to the offset direction of the center of the guide groove of the inner joint member. In this case, under the pressing force of the elastic member applied thereto, the inner joint member makes a relative displacement in the axial direction opposite to the offset direction of the guide groove thereby to press the torque transmitting ball, and stops at a position where the inner clearance between the torque transmitting ball and the guide grooves (ball track) of the inner and outer joint members disappears. As a result, a certain amount of preload is applied in the axial direction to the torque transmitting balls, thus eliminating the rotation backlash (play in the circumferential direction).
Regions that are free of undercut may be provided in the guide grooves of the outer joint member and the inner joint member. This makes it possible to increase the operating angle of the joint.
The region on the opening side of the inner circumferential surface of the outer joint member may be formed in a cylindrical surface that fits with the outer circumferential surface of the cage. This makes it easier to assemble the cage into the outer joint member.
The constant velocity universal joint of the present invention is light in weight, small in size and low cost, and rotates smoothly without backlash with less resistance to rotation, while being capable of taking a large operating angle, and is therefore particularly preferable for the steering apparatus of an automobile.